Some examples for process control charts



Some examples for process control charts

Bolts produced with mean length 7.65 mm, standard deviation .10 mm (when process is in control). Samples of 30 bolts (at a time) to be taken at hourly intervals during the production.

Process mean: 7.65, LCL = 7.65 - 3(.10/) = 7.60 UCL = 7.65 + 3(.10/) = 7.70

10 samples: x= 7.61, 7.72, 7.66, 7.64, 7.68, 7.69, 7.68, 7.63, 7.69, 7.72

[pic]

Setting up chart from sample data (process known in control)

Weight of contents of a "10 oz" bag of candy

set-up data (process known to be in control)6 samples, 20 bags in each:

x 10.21 10.22 10.17 10.18 10.26 10.28

R (oz) .19 .26 .19 .28 .20 .13

x= 10.22 R= .21 d2 = 3.735 A2 = .180 so σ ≈ .21/3.735 ≈ .06 and

LCL = 10.22 - .180 (.21) = 10.18 UCL = 10.22 + .180 (.21) = 10.26

[pic]

R chart

Weight of contents of a "10 oz" bag of candy

set-up data (process known to be in control)6 samples, 20 bags in each:

x 10.21 10.22 10.17 10.18 10.26 10.28

R (oz) .19 .26 .19 .28 .20 .13

x= 10.22 R= .21 d2 =3.375 d3 = 0.729 D3 = .415 D4 = 1.585 and

LCL = .21(.415) = .09 UCL = .21(1.585) = .33

[pic]

p chart:

Proportion of defective transistors in lots of 150 transistors. ,

10 samples of 150 each,

sample # 1 2 3 4 5 6 7 8 9 10

# defectives 10 5 8 14 12 2 1 9 13 13

sample p .067 .033 .053 .093 .080 .013 .007 .06 .087 .087

pooled p = [pic]

so [pic] LCL = .001 UCL = .077

[pic]

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